Magnetic Properties of Phospho-Olivine Li(Fe $_{1-x}$ Mn $_{x}$ )PO

The crystalline structure of the Li(Fe_1-xMn_x)PO₄ (x = 0.0, 0.2) samples was determined to be olivine-type orthorhombic with Pnma space group. The contraction ofunit cell volume from LiFe_0.8Mn_0.2PO₄ (V = 293.296 ų) to LiFePO₄ (V = 291.445 ų) can be explained by the different ionic radii of high-spin Fe²⁺ and Mn²⁺. The temperature-dependent magnetic susceptibility and Curie-Weiss fitted reciprocal susceptibility curves of Li(Fe_1-xMn_x)PO₄ indicates that there are antiferromagnetic ordering with different values of magnetic Neel temperature and effective moment between LiFe_0.8Mn_0.2PO₄ (T_N = 49 K, μ_eff = 5.66μ_B) and LiFePO₄ (T_N = 51 K, μ_eff = 5.37 μ_B). From the Mossbauer analysis, The distribution of the Mn²⁺ (3d₅) ions in M₂ magnetic sites can lead to the reduction of magnetic hyperfine field (H_hf) of LiFe_0.8Mn_0.2PO₄ in Fe²⁺ (3d₆) sites. Also, the isomer shift (δ) and electric quadrupole splitting (ΔE_Q) values, increasing with Mn²⁺ substitution, can be attributed to the decrease of charge density at Fe nucleus ρ_A (0) due to the 3d-electron penetrating closer to the Fe nucleus with asymmetric charge distribution by the presence of Mn²⁺ ions on the FeO₆ octahedral sites.